Inspection of welds in pressure vessels is important to ensure the proper maintenance of the pressure vessel. One particular problem which requires attention is that of testing the circumferential welds in boiler pipes. Such pipes are arranged in an array of side by side pipes with only a very small clearance between each pipe and the next. Such pipes have a number of circumferential welds which require to be inspected, bearing in mind that the pipe can only be accessed from a front face so that the rear face of the pipe and the rear part of the weld is difficult to access.
Ultra-sonic transducers have become available which carry out an inspection of the weld and require to be transported along the length of the weld that is angularly around the axis of the pipe so as to extend along the full 360° of the circumferential weld. The ultra-sonic transducers have been designed so that they lie primarily along the length of the pipe so that the transducer itself can pass between the pipes as its height from the surface of the pipe is relatively small.
Two such transducers are required so that each lies along the pipe with a head of the transducer immediately adjacent the respective side of the weld. These transducers are then carried around the pipe and it is desirable that the position of the transducers angularly around the pipe is carefully monitored so that the signal from the transducers can be coordinated with the position of the transducers angularly of the pipe to provide a signal which locates any faults in the weld and their position angularly of the pipe.
The transducers have a cable which extends from one side of the transducer to carry the signals from the transducer to a remote control and monitoring system. The transducers also include a liquid supply which generates a film between the head of the transducer and the weld of the pipe or the pipe surface so that the sound waves are effectively transmitted between the transducer head and the pipe itself.
The requirement therefore is to provide an apparatus which can be readily mounted on the pipe at the position adjacent the weld and which carries the transducers and rotates those transducers around the pipe, bearing in mind that effective access to the pipe is generally only available from one side of the pipe.